The present invention is directed to a method and system for monitoring tire pressure in a vehicle equipped with an anti-lock braking system (ABS) based on the deviation of tire pressure of at least one tire from a reference value.
Safety and reliability are central aspects of automotive engineering. Tire pressure is an important aspect in this regard. Loss of tire pressure has been recognized to be a significant factor in road traffic accidents. 85% of tire failures are a consequence of a creeping pressure loss. Incidentally, correctly adjusted tire pressure ensures optimal driving comfort at all times in terms of rolling noise, vertical bumpiness and sensitivity to transverse expansion joints.
It is known that tire pressure can be monitored directly by means of pressure sensors on two-axle or three-axle vehicles (see ATZ Automobiltechnische Zeitschrift 102 (2000) 11, pp. 950 ff.). The pressure sensors are mounted on the tire and rotate with the wheel. The pressure sensors are equipped with a high-frequency transmitter (HF transmitter) which transmits the measured pressure values to a receiver disposed in the motor vehicle and signals pressure losses to the driver. This functions both during travel and when the vehicle is stationary. Since this approach is based purely on measurement, the costs are relatively high, especially if all wheels are being monitored.
It is also known that tire pressure can be monitored indirectly by means of ABS wheel sensors (see ATZ Automobiltechnische Zeitschrift 94 (1992) 6, pp. 336-340; EP 0 489 562 B1; EP 0 489 563 B1 and EP 0 607 690 B1). Tire pressure also affects the rolling circumference of the tires. The speed of rotation of the wheels determined by means of the wheel sensors of the ABS depends on the rolling circumference of the wheels. If, during travel in a straight line without braking, the speed of rotation of a wheel changes relative to the reference speed of the other wheels or of one other wheel, this represents an indicator of a change in rolling circumference of the wheel in question as a result of pressure loss from the tire or of separation of pieces of tire at the tire circumference or of a variation in loading. Any change of rolling circumference is interpreted as a pressure change.
The known methods of monitoring tire pressure are imprecise and are capable of detecting only large and suddenly occurring pressure changes.
Accordingly, it is desired to provide a method and system for monitoring tire pressure that permit detection of small and creeping tire pressure losses.
Generally speaking, in accordance with the present invention, a method and system for monitoring vehicle tire pressure are provided which overcome disadvantages associated with prior art methods and systems.
The tire pressure monitoring system and method according to the present invention are provided for vehicles equipped with anti-lock braking systems, especially vehicles having more than two axles. ABS wheel sensors on the wheels of at least one axle sense variables which depend on wheel rotation such as the travel distances covered by the wheels or the speeds of rotation of the wheels. An ABS control unit adds the variables of the individual wheels on the respective diagonals relative to the wheel arrangement of the vehicle. Recognition of an undesired (insufficient) tire pressure condition takes place when the diagonal sums differ from one another by more than a preselected limit value. Furthermore, monitoring of the variables takes place in a plurality of monitoring cycles, recognition of an undesired tire pressure condition taking place when the deviations of the diagonal sums exceed a summation limit value defined for all monitoring cycles. Thus, it is possible to achieve improved accuracy and sensitivity in the recognition of undesired tire pressure conditions.
An embodiment of the present invention utilizes a combination of direct tire pressure measurement by means of pressure sensors of a tire pressure measuring system and indirect tire pressure determination using the wheel sensors. It is therefore possible to substitute pressure sensors of the tire pressure measuring system by ABS wheel sensors and/or to use the ABS control device for evaluation of the measured signals of the tire pressure measuring system as well, whereby components and costs can be saved without impairing the reliability and safety of tire pressure monitoring. The actual tire pressures determined by means of pressure sensors support the values determined indirectly by means of the ABS.
Accordingly, it is an object of the present invention to provide a method and system for monitoring tire pressure in vehicles, including vehicles equipped with ABS.
It is also an object of the present invention to provide a method and system for tire pressure monitoring that are cost-effective and that react more sensitively to small and creeping pressure losses.
It is another object of the present invention to provide a method and system for tire pressure monitoring which provide for both direct and indirect pressure determination.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combination of elements, and arrangement of parts which are adapted to effect such steps, all as exemplified in the detailed disclosure hereinafter set forth, and the scope of the invention will be indicated in the claims.